Blasting through the Darkness: Worms with the Power of Illumination

One of the most famous characteristics of the deep is the beautiful display of light some organisms are able to emit known as bioluminescence. It has grasped the attention of many scientists, including Charles Darwin who claimed to see ‘milky seas‘ (similar to Figure 1) on his voyage on the HMS Beagle (1832-1836) as well as flashes of light from jellyfish, and the glow from the glow-worms in South Africa. In the film Mission Blue, Sylvia Earle, currently one of the world’s most famous and influential marine biologists, dived down to 380 m to what was expected to be complete darkness. Yet it was not darkness she found rather “thousands of sparkles and flashes everywhere” claiming it to “amazing” and she was “as excited a little child”.

Figure 1 Bioluminescent phytoplankton giving off a blue coloured glow in the darkness of night on a beach on Vaadhoo Island, Maldives. Darwin encountered similar sightings on his voyage of the HMS Beagle and documented such bioluminescence as ‘seeing Milky Seas’ (photographed by Doug Perrine)

A recent study suggested up to 90% of the organisms of the deep are able to produce light. It is thought to be so common because the deep sea is a very stable environment with temperature, light intensity and salinity and all other conditions remaining unchanged for decades.

The Deep Dark Sea

The deepest part of the ocean is so deep it could cover 25 Empire State Buildings standing tall (over 4000 m). ‘Deep sea’ begins at the mesopelagic zone (also known as the ‘twilight’ zone) between a depth of 200-1000 m. Below this are the bathypelagic, abyssopelagic and hadopelagic zones which are all in complete darkness as no light can penetrate to these depths. This zonation is shown in Figure 2.

Figure 2 The image shows the layers of the ocean in relation to depth. Mesopelagic begins at 200m deep and is classed as ‘deep sea’ (Image taken from Sea and Sky).

How do the organisms emit the light?

Bioluminescence is a result of a chemical reaction in an organism that results in the production of photons. It requires two molecules: Luciferin and either Luciferase or Photoprotein. In one reaction the enzyme Luciferase interacts with the compound Luciferin. When oxygen is added to this reaction, it creates a byproduct called oxyluciferin which creates the light emitted by these organisms. However, some organisms cannot produce the enzyme Luciferase, instead they use a chemical known as a Photoprotein. In this reaction, Luciferin combines with oxygen and with the help of another agent, such as a calcium ions or a magnesium ions, light is produced. Most marine organisms at such depths are limited to only seeing blue-green wavelengths (410 nm – 720 nm); most marine bioluminescence is the green-blue part of the visible light spectrum. Most species are unable to process other wavelengths such as the yellow, red or violet parts of the spectrum.

The ‘Green Bombers’ of the deep sea

In 2001, a novel group of worms, Swima, were discovered in the deep-sea (2732-3600 m) off the Californian and Oregon Coast. The most well-known species of the Acrocirridae genus is Swima bombiviridis who were given the nickname ‘green bombers’ due to their highly adapted ability to release a green bioluminescent ‘bomb’. Figure 3 shows Swima bombiviridis seconds after its ‘bombs’ have been released .

Figure 3 Swima bombiviridis is able to drop up to eight ‘green bombs’ which are all filled with a bioluminescent liquid. These worms are up to 30mm long and their ‘bombs’ are 1-2 mm diameter. Credit: BBC

The pelagic Swima bombiviridis are an exceptionally unique species who lack eyes, have over 30 long spinous chaetae per parapodium used for swimming, have a transparent foregut and a thick gelatinous sheath which is penetrated by long, club-shaped papillae. Yet the most valuable asset they have are their branchiae. They have 3 forms of branchiae;

This last set of branchiae are the most important as these are the so called ‘green bombs’ they release. They have eight (4 pairs) of these bombs growing on the basal part of the nephridiopore papillae (shown in the video below). The most recent research suggests the bombs are filled with a simple, fluid or mucus which contain unorganised clusters of bioluminating particles. These bombs are approximately 1-2mm diameter consisting of 2 small central chambers and 2 very small hemolymph– filled chambers.

As explained in the video, it is assumed these bombs are detached when used as a defence mechanism when the worm feels threatened. A similar adaptation is used in the Vampire Squid, Vampyroteuthis infernalis, when it releases bioluminescent ink to scare predators, allowing it to escape. When a predator approaches, the ‘green bombers’ detach the bombs which intensely glow for several seconds before diminishing. This glow is believed to periodically startle the predators whilst the worm escapes.

The research on the newly discovered clade of annelid worms is quite limited as they are difficult to study in situ as it requires very technical machinery to get to such depths. Furthermore, fact that their discovery is so recent stresses how little knowledge we have of the deep sea and how much more opportunity we have to develop our understanding of the deep sea.

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3 Comments Already

Jack Buckingham-November 10th, 2016 at 20:53none
Comment author #79 on Blasting through the Darkness: Worms with the Power of Illumination by Extreme Marine

Hiya- great topic and an interesting read! I think you got the balance of scientific content and readability just right. I particularly liked how most of your subheadings were questions which you then answered with the following paragraph. Also its got a good structure- broad topic at the beginning, focus in the middle and then widening it out with the bigger picture at the end with the uses to humans paragraph, which is always a good topic to include! Perhaps a hyperlink to related research in that last paragraph would have been good. Also watch out for the odd typo and capital letter where you don’t need one. Other than that the only other advice I can think of is, as it’s such a popular topic, a more eye-catching title would help it stand out a little more- but other than that you’re grand. 🙂

Charlotte Walker-November 13th, 2016 at 12:21none
Comment author #114 on Blasting through the Darkness: Worms with the Power of Illumination by Extreme Marine

Interesting article, was intrigued to find out more about this topic. The pictures were good and were definitely relevant but could have been linked into the text more and also have citations or references. The way your sub headings were questions aided the flow and made it easy to read and follow. I thought that the last paragraph had interesting points and could have been expanded a bit more or more conclusive. But overall I thought it was a really good article!

Callum Timms-November 13th, 2016 at 18:46none
Comment author #128 on Blasting through the Darkness: Worms with the Power of Illumination by Extreme Marine

The article was well written, however there was a lack of citations and the images did not really tie in with what you said. It was quite concise, whether or not that is a bad thing is up to the individual. It was an enjoyable read none the less

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